Oil and gas wells are now being drilled in water which is so deep that fixed drilling platforms are not suitable and floating platforms are used. These floating drilling platforms have some movement responsive to wind, waves and current. Current also acts on the drilling conduit or riser. With drilling proceeding in relatively deep water, the riser due to its increased length and resulting greater weight must be tensioned at the drilling vessel as well as buoyed along its length to prevent buckling. The movement of the drilling vessel and the current forces on the riser create dynamic loads on the riser which produce alternating stresses therein.
Prior riser connectors are preloaded at initial make-up but the preloading is not sufficient to avoid wear of mating parts as a result of movement. The life of present riser connectors is greatly shortened by the combination of the alternating stresses on the riser connector and its stress concentration factors. Another disadvantage experienced by prior preloaded riser connectors is that they have been extremely heavy and expensive. In certain of these riser connectors extremely high preloads are used to accommodate the high thermal gradients resulting from hot fluids in the riser and cooler seawater around the riser which tend to relieve the preload. Also, large oil flow lines have high thermal gradients in which loaded connectors are desirable, particularly a connector in which the thermal gradients do not relieve the preload.
The Luke et al U.S. Pat. No. 4,012,059 discloses a pipe connector having telescoping tubular members with one of the members being stretchable to preload the latch means. The latches include a plurality of ring segments which engage in grooves between the two members to retain them in loaded position. The J. Moon U.S. Pat. No. 2,485,763 discloses a tool joint and collar assembly which includes fingers engaging on a shoulder and a sleeve or collar which slides onto the fingers to hold them in engaged position. The Van Bilderbeek et al U.S. Pat. No. 4,074,912 discloses a rigid pile connector which includes a ring engaged by a plurality of buttons from one member, and a plurality of fingers engaging an internal shoulder on the other member with the interior of the fingers held in place by a removable sleeve.
Preloaded connectors are shown in the Jansen U.S. Pat. No. 4,093,281 and the Ahlstone U.S. Pat. No. 4,124,229 which disclose the use of hydraulic cylinders for preloading the joint. Jansen suggests threading a reaction nut against the members during loading to retain the loading after the cylinders are released. Ahlstone provides a pressure energized shrink fit.